Microfluidics involve the control and manipulation of fluids at a small scale. Using microfluidics, fluids can be moved, mixed, separated, or otherwise processed. One particularly popular area of microfluidics is droplet microfluidics, which involves manipulating discrete volumes of fluids. Systems that use droplet-based microfluidics include, for example, fast analytical systems or the synthesis of advanced materials to protein crystallization and biological assays for living cells. Conventional droplet generation and manipulation devices and methods, however, suffer from various shortcomings. Accordingly, there is a continuing need from improved devices and methods for generating and manipulating droplets.